1. Field of the Invention
The present invention relates to a process for the preparation of polyether-ester polyols. More particularly, the invention relates to the preparation of these polyols by reacting a polyether polyol, maleic anhydride and an alkylene oxide in the presence of an effective amount of a catalyst selected from the group consisting of calcium naphthenate and cobalt naphthenate.
2. Description of the Prior Art
The preparation of polyether-ester polyols by the reaction of an alkylene oxide with a half acid ester obtained by the reaction of a polyol with an unsaturated acid anhydride is well known in the art as taught in U.S. Pat. Nos. 3,931,092, 4,014,846, 4,093,573 and 4,144,395. These patents relate to uncatalyzed or trialkylaminecatalyzed reactions. U.S. Pat. No. 3,374,208 teaches the use of various metal catalysts for the preparation of polyesters. The prior art, however, does not teach the preparation of polyether-ester polyols having an acidity of less than 5 mg KOH/gm of sample employing the process of the instant invention.